If true, this parameter causes the modifications in this request and any pending modifications to be applied, asynchronously and as soon as possible, regardless of the PreferredMaintenanceWindow setting for the cache cluster.
If false, then changes to the cache cluster are applied on the next maintenance reboot, or the next failure reboot, whichever occurs first.
If you perform a ModifyCacheCluster before a pending modification is applied,
the pending modification is replaced by the newer modification.
Valid values: true | false